1. Technical Field
The present disclosure relates to an illumination control circuit. More particularly, the present disclosure relates to an illumination control circuit with dimming functions.
2. Description of Related Art
With recent developments in photonics technology, many cutting-edge illumination devices are being used in our daily lives. For example, there has been significant development with respect to fluorescent lamps and light-emitting diodes (LEDs) and their applications.
An LED lamp has an efficiency superior to a traditional incandescent lamp, because most of the energy consumed by an LED lamp is transformed into visible radiation. As a result of its high efficiency (i.e., high photoelectric conversion efficiency), which is far higher than that of other lamps, the LED lamp generates less heat during operation. Stated differently, for the same luminance, an LED lamp has a lower operating temperature than that of a traditional incandescent lamp. Therefore, the LED lamp is in line with green energy trends and is widely used in all kinds of illumination applications.
Traditional incandescent lamps may be used in cooperation with a tri-electrode alternating-current switch (TRIAC) dimmer, so that users can conveniently adjust the luminance of the incandescent lamps, allowing less energy to be used and permitting alleviation of any eye discomfort due to over-brightness. A TRIAC dimmer typically includes a variable resistor, in which a resistance can be adjusted by a user (e.g., by rotating a knob of the TRIAC dimmer). In this way, users are able to control a conductive angle of the TRIAC, so as to change an output waveform of the TRIAC.
The dimming function of a TRIAC dimmer is realized in a phase-chopping manner. Reference is made to FIG. 1, which is a schematic diagram illustrating a dimming signal waveform generated by a traditional TRIAC dimmer. In FIG. 1, the waveform generated by the TRIAC dimmer is chopped according to its phases, and the dimming result is related to the conductive angle of the phase-chopping.
The TRIAC dimmer is mainly used for a resistive load (e.g., a fluorescent lamp). However, an LED lamp is a non-resistive load. When a traditional TRIAC dimmer is directly utilized to control the luminance of an LED lamp, the relationship between an output voltage (or current) of the dimming signal and the conduction angle of the dimming signal will be non-linear. This will cause non-linear distortion, especially when the conduction angle is small.
Currently, LED devices utilize specific LED drivers for transforming household electricity into a fixed DC voltage signal, which is used to drive the light-emitting component in an LED for illumination. Such a DC voltage signal is set at a fixed voltage level, and as a result, luminance cannot be adjusted easily. For the sake of energy conservation and to allow user adjustability of brightness, there is a need to develop LED illumination devices that have a practical dimming function.